It carries 3 proofs.
Initially 1887 - 1896 and as noted 13/1 = bore of .719" - .728"

2nd proof was 1925-1954 when the chamber length and 1 1/8 oz. were 1st marked.
The Birmingham Proof date code at the top was used 1921-1942 and if you could chalk the mark maybe the capital letter at the top could be deciphered

3rd proof was 1954 - 1989 at 3 TONS, for a service pressure of about 9000 psi.
Bore now .729", chamber length 2 1/2" and Crowned BNP
The date code is bottom used 1950 - 1974. If you can read the capital letter on the left that would be the year. That is likely when it was sleeved.

[Linked Image from photos.smugmug.com]

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